1. Field of the Invention
The present invention relates to a zoom lens and an electronic image pickup apparatus equipped with the same, and in particular to an electronic image pickup apparatus, such as a video camera and a digital camera, in which reduction in the depth is achieved by an inventive optical design of a zoom lens and a zoom lens used in the image pickup apparatus.
2. Description of the Related Art
Nowadays, film cameras are not the mainstream, and digital cameras that pick up an image of an object using a solid state image pickup element such as a CCD or CMOS sensor have replaced film cameras to become the mainstream. Digital cameras are not limited to one category, but there are a number of categories of digital cameras ranging from popular-priced compact type cameras to high-class function-rich cameras. The present invention can suitably be applied, among others, to compact type digital cameras.
Users of such compact type digital cameras generally wish to enjoy easy and simple shooting in wide-ranging shooting situations anywhere at any time. For this reason, such users favor small size digital cameras, in particular cameras that are small with respect to the thickness direction (i.e. depth) and can be conveniently carried in a pocket of clothes or a bag. For the same reason, a further reduction in the size of the taking lens system is demanded.
Meanwhile, there is a trend toward increases in the number of pixels of image pickup elements, and zoom lenses are required to have high optical performance matched with the increased number of pixels of image pickup elements. Apart from such needs of users, it is necessary for digital camera manufacturers to keep the production low and to achieve a high mass productivity in order to make profits. To this end, it is necessary to reduce the sensitivity of deterioration in optical performance to production errors occurring in the process of manufacturing and assembling of lenses.
Zoom lenses having high zoom ratios of 7 to 10 or more have become popular, because they can be used in a wider variety of shooting situations. While there is a demand for further increases in the zoom ratio, there also is a demand for wider angles of field that enable easy shooting of indoor scenes. To meet such demands of users, various types of zoom lens systems have been developed.
As a relatively compact prior art zoom lens matched with an image pickup element having a large number of pixels, there is a known type of zoom lens, which includes, in order from the object side thereof, a positive first lens unit, a negative second lens unit, a positive third lens unit, a positive fourth lens unit, and a positive fifth lens unit, as disclosed in Japanese Patent Application Laid-Open No. 2005-107273. In this zoom lens, the first lens unit is composed of a cemented lens made up of a positive lens and a negative lens, which enables good correction of on-axis chromatic aberration while making the zoom lens compact.
There is another prior art zoom lens system, which includes, in order from the object side thereof, a positive first lens unit, a negative second lens unit, a positive third lens unit, a positive fourth lens unit, and a positive fifth lens unit, as disclosed in Japanese Patent Application Laid-Open No. 2005-55625.
This zoom lens has a zoom ratio of about 4, and on-axis and off-axis aberrations therein are corrected excellently.
As another prior art, Japanese Patent Application Laid-Open No. 2007-10695 discloses an optical system including, in order from the object side thereof, a positive first lens unit, a negative second lens unit, a positive third lens unit, a positive fourth lens unit, a positive fifth lens unit and having a zoom ratio of as high as 20. This optical system has two positive lenses in the third lens unit, whereby relatively good optical performance is achieved though the optical system has a very high zoom ratio of 20.